Cationic bactericides such as benzethonium chloride and cetylpyridinium chloride are incorporated in many compositions for the oral cavity because they have high bactericidal activity against oral bacteria, readily adsorb to the surface of the oral tissues such as the teeth and the oral mucosa, and prevent the formation of biofilms such as plaque and tongue coating.
Cationic bactericides, on the other hand, usually have a strong unpleasant taste such as bitterness so that an oil-soluble flavor is used in combination therewith in order to mask such a taste and improve the feeling upon use. When an oil-soluble flavor is incorporated, a solubilizer such as an anionic or nonionic surfactant is used as an essential component, but such a surfactant or an oil-soluble flavor tends to impair the adsorption of the cationic bactericide to the surface of the oral tissues such as the teeth and the oral mucosa. A technology of preparing a composition for the oral cavity without adding thereto an oil-soluble flavor or surfactant is reported (Patent Document 1) as a method of overcoming such an inconvenience, but this technology has problems that because of a water-soluble flavor used instead of the oil-soluble flavor, the resulting composition lacks a cooling sensation and has less freedom of choice in the design of its taste. In addition, the technology of solubilizing an oil-soluble flavor with a small amount of surfactant is proposed (Patent Document 2). Owing to a polyoxyethylene-added nonionic surfactant used in this technology, the adsorption of the cationic bactericide to the surface of the oral tissues such as teeth and oral mucosa is not always sufficient. Further, the technology of adding polyoxyethylene polyoxypropylene glycol which is a nonionic surfactant in order to bring out the effect of the bactericide fully (Patent Document 3) is proposed. This technology however has a problem that owing to the insufficient solubilizing power of the surfactant, the surfactant added in an amount enough to obtain a transparent and stable liquid composition impairs the cooling sensation of the oil-soluble flavor.    [Patent Document 1] JP-A-07-101842    [Patent Document 2] JP-A-2001-302478    [Patent Document 3] JP-A-04-202121